Utilization of invertebrates discarded from the Nephrops fishery by variously selective benthic scavengers in the west of Scotland

mbergmann [ at ] awi-bremerhaven.de


Demersal trawl fisheries generate large quantities of discards which temporarilyincrease the amount of carrion available to benthic communities and lead to a faster energetic turnover.This study examines the availability of discarded material to the benthos, assesses consumptiontimes of different items and identifies scavengers attracted to those invertebrates most frequently discardedfrom Clyde Sea Nephrops trawlers. In field and laboratory trials, heavy-shelled dead whelks(Buccinum undatum, Neptunea antiqua) sank faster than softer-bodied species like cephalopods(Allotheuthis subulata, Rossia macrosoma) or echinoderms (Ophiura ophiura, Asterias rubens), makingmost discards available to the benthos (at ca. 60 m CD [chart datum]) within minutes after discarding.SCUBA and time-lapse camera observations in the Clyde Sea and Loch Sween indicatedbait utilisation times between 24 and 48 h. Fast-moving animals like brachyuran crabs were the firstto arrive at discard bait piles whose composition mimicked typical discards from the Clyde SeaNephrops fishery. Bimonthly deployments of traps baited with invertebrate discards in the north ofthe Clyde Sea showed that A. rubens, followed by Pagurus bernhardus, Liocarcinus depurator andwhelks, were the most abundant megafaunal scavengers. Fine-meshed funnel traps deployed insidethose creels yielded up to 2819 amphipods per trap, with Scopelocheirus hopei and Orchomenenanus accounting for most of the catch. Together with whelks, A. rubens and Carcinus maenas,O. nanus showed a clear preference for crustacean bait. By contrast, Pagurus bernhardus was moreattracted to A. rubens and, in 1 trial, to O. ophiura bait. Traps deployed in the south of the Clyde Seayielded generally lower numbers and species diversity in the catch, with Nephrops being the mostabundant megafaunal scavenger. It showed a preference for L. depurator and conspecific bait. Whilethe results show that a range of epibenthic species readily utilise invertebrates discarded from ClydeSea Nephrops trawlers, it is unknown to what extent discards subsidise benthic communities as informationon the ecological energetics of the species involved locally is currently lacking.

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Bergmann, M. , Wieczorek, S. K. , Atkinson, R. J. A. and Moore, P. G. (2002): Utilization of invertebrates discarded from the Nephrops fishery by variously selective benthic scavengers in the west of Scotland , Marine Ecology-Progress Series, 233 , pp. 185-198 .

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